The present invention relates generally to gas turbine engines, and, more specifically, to brush seals therein.
In a gas turbine engine, air is compressed in a compressor, mixed with fuel in a combustor and ignited for generating hot combustion gases which flow downstream to one or more turbine stages which extract energy therefrom. Both the compressor and the turbine stages include stationary vanes cooperating with rotating blades for compressing and expanding in turn the compressed air and combustion gases, respectively. The compressed air and combustion gases vary in pressure through the engine and various seals are provided for maintaining differential pressure between the various components of the engine for maximizing performance efficiency thereof.
For example, a turbine rotor is typically sealed relative to a cooperating stator so that the rotor may be pressurized in the forward direction of the engine for providing thrust balancing in opposition to the aft directed force generated in a low pressure turbine. An annulus between the rotor and stator may include a brush seal in one or more stages for providing effective sealing therebetween.
A typical brush seal includes a pack of wire bristles inclined relative to the rotation of the rotor, with distal ends of the bristles contacting the rotor for maintaining a seal therewith. The bristle pack is supported between forward and back plates for providing structural integrity of the bristles which are relatively flexible for accommodating differential thermal movement between the stator and the rotor during operation. The bristles are subject to vibration due to movement of the pressurized fluid being sealed thereby. For example, the rotor induces a circumferential component of velocity of the pressurized fluid which engages the bristles causing excitation thereof.
In order to dampen vibration of the bristles during operation, an annular damper plate is typically provided to sandwich the bristle pack against the back plate leaving exposed only a small portion of the bristles at their distal ends for contacting the rotor. An exemplary damper plate includes an annulus of thin sheet metal having a plurality of circumferentially spaced apart radial slits extending outwardly from the inner diameter thereof to circumferentially segment the damper plate for accommodating differential thermal expansion and contraction. However, the individual tabs defined between the slits are themselves subject to flow induced flutter which may lead to high cycle fatigue damage of the damper plate itself, and in turn the bristles therebelow.
Accordingly, a brush seal having an improved damper is desired for increasing damping effectiveness and increasing useful life during operation.